Image forming apparatuses such as digital copiers, laser printers, or facsimile machines are widely used. Such an image forming apparatus uses an image writing device that scans a laser beam to write an image on a photoreceptor. When an image forming apparatus forms an image, a charging device charges a photoreceptor and the image forming apparatus then performs writing in accordance with image information to form an electrostatic latent image on the photoreceptor. The electrostatic latent image on the photoreceptor is developed with toner supplied from a developing device. The toner image developed on the photoreceptor is transferred onto a recording paper sheet by a transferring device and is fixed on the recording paper sheet by a fixing device to acquire a desired image.
Along with speeding up of color image forming apparatuses such as digital copiers and laser printers, a tandem-mode apparatus is in practical use which includes a plurality of photoreceptors in tandem arrangement. In this case, for example, four photoreceptor drums are arranged in the carrying direction of the recording paper; the photoconductors are concurrently exposed to light by a scanning optical system corresponding to the photoconductor drums to form latent images; and these latent images are developed by developing devices that use developer with different colors such as yellow (Y), magenta (M), cyan (C), and black (K). The developed toner images are sequentially transferred and overlapped on the same recording paper sheet to acquire a color image.
Electrophotographic image forming apparatuses generally use developers such as toners and the toners drop and scatter within the image forming apparatuses. Therefore, a laser exposure device having optical components for exposing a photoconductor disposed within a housing is used to shield the optical components from the toners and other dusts.
Such a laser exposure device has optical components such as laser diodes and polygon mirrors disposed within the housing and YMCK light beams are emitted from the housing to expose a photoreceptor drum disposed outside the housing.
Therefore, the housing of the laser exposure device is provided with an emission window made of light-transmitting material for transmitting a laser beam emitted outside to close the housing even at the portion of the light emitting path for the laser beam.
However, since the emission window portion is exposed to the environment with dropping toner on the outside, it is problematic that the toner adheres to and contaminates the outer surface of the emission window, reduces the transmissivity of the light beam, and reduces quality of images to be formed.
With regard to such a problem, Japanese Laid-Open Patent Publication No. 2005-329622 discloses an apparatus provided with a shutter such that the emission window is not contaminated by toner, etc. A covering member is provided that is movable to a covering position for covering the light transmitting dust-proof member for closing the opening part formed in the optical housing, and to an opening position for opening the covering of the light transmitting dust-proof member. A cleaning member is fitted to the covering member and is brought into slidable contact with the outer peripheral face of the light transmitting dust-proof member when the covering member is moved. Before starting an image forming action and after finishing it, the covering member is moved, and the dust stuck on the outer peripheral face of the light transmitting dust-proof member is automatically cleaned by the cleaning member.
If the outer surface of the light-transmitting emission window disposed on the housing of the laser exposure device is contaminated, it is problematic that the transmissivity of the light beam is reduced and that the quality of images to be formed is reduced as described above. To solve this problem, an apparatus is desired that hinders toner from adhering to the outer surface of the emission window and enables immediate cleaning if the toner adheres. Because of the request for miniaturization of image forming apparatuses, the emission window must be prevented from being contaminated and the cleaning must be done without increasing the size of the apparatuses.